PPCAsmBackend.cpp

//===-- PPCAsmBackend.cpp - PPC Assembler Backend -------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include "MCTargetDesc/PPCFixupKinds.h"
#include "MCTargetDesc/PPCMCTargetDesc.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/BinaryFormat/MachO.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCELFObjectWriter.h"
#include "llvm/MC/MCFixupKindInfo.h"
#include "llvm/MC/MCMachObjectWriter.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSectionMachO.h"
#include "llvm/MC/MCSubtargetInfo.h"
#include "llvm/MC/MCSymbolELF.h"
#include "llvm/MC/MCSymbolXCOFF.h"
#include "llvm/MC/MCValue.h"
#include "llvm/MC/TargetRegistry.h"
#include "llvm/Support/ErrorHandling.h"
using namespace llvm;

static uint64_t adjustFixupValue(unsigned Kind, uint64_t Value) {
  switch (Kind) {
  default:
    llvm_unreachable("Unknown fixup kind!");
  case FK_Data_1:
  case FK_Data_2:
  case FK_Data_4:
  case FK_Data_8:
  case PPC::fixup_ppc_nofixup:
    return Value;
  case PPC::fixup_ppc_brcond14:
  case PPC::fixup_ppc_brcond14abs:
    return Value & 0xfffc;
  case PPC::fixup_ppc_br24:
  case PPC::fixup_ppc_br24abs:
  case PPC::fixup_ppc_br24_notoc:
    return Value & 0x3fffffc;
  case PPC::fixup_ppc_half16:
    return Value & 0xffff;
  case PPC::fixup_ppc_half16ds:
  case PPC::fixup_ppc_half16dq:
    return Value & 0xfffc;
  case PPC::fixup_ppc_pcrel34:
  case PPC::fixup_ppc_imm34:
    return Value & 0x3ffffffff;
  }
}

static unsigned getFixupKindNumBytes(unsigned Kind) {
  switch (Kind) {
  default:
    llvm_unreachable("Unknown fixup kind!");
  case FK_Data_1:
    return 1;
  case FK_Data_2:
  case PPC::fixup_ppc_half16:
  case PPC::fixup_ppc_half16ds:
  case PPC::fixup_ppc_half16dq:
    return 2;
  case FK_Data_4:
  case PPC::fixup_ppc_brcond14:
  case PPC::fixup_ppc_brcond14abs:
  case PPC::fixup_ppc_br24:
  case PPC::fixup_ppc_br24abs:
  case PPC::fixup_ppc_br24_notoc:
    return 4;
  case PPC::fixup_ppc_pcrel34:
  case PPC::fixup_ppc_imm34:
  case FK_Data_8:
    return 8;
  case PPC::fixup_ppc_nofixup:
    return 0;
  }
}

namespace {

class PPCAsmBackend : public MCAsmBackend {
protected:
  Triple TT;
public:
  PPCAsmBackend(const Target &T, const Triple &TT)
      : MCAsmBackend(TT.isLittleEndian() ? llvm::endianness::little
                                         : llvm::endianness::big),
        TT(TT) {}

  unsigned getNumFixupKinds() const override {
    return PPC::NumTargetFixupKinds;
  }

  const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const override {
    const static MCFixupKindInfo InfosBE[PPC::NumTargetFixupKinds] = {
      // name                    offset  bits  flags
      { "fixup_ppc_br24",        6,      24,   MCFixupKindInfo::FKF_IsPCRel },
      { "fixup_ppc_br24_notoc",  6,      24,   MCFixupKindInfo::FKF_IsPCRel },
      { "fixup_ppc_brcond14",    16,     14,   MCFixupKindInfo::FKF_IsPCRel },
      { "fixup_ppc_br24abs",     6,      24,   0 },
      { "fixup_ppc_brcond14abs", 16,     14,   0 },
      { "fixup_ppc_half16",       0,     16,   0 },
      { "fixup_ppc_half16ds",     0,     14,   0 },
      { "fixup_ppc_pcrel34",     0,      34,   MCFixupKindInfo::FKF_IsPCRel },
      { "fixup_ppc_imm34",       0,      34,   0 },
      { "fixup_ppc_nofixup",      0,      0,   0 }
    };
    const static MCFixupKindInfo InfosLE[PPC::NumTargetFixupKinds] = {
      // name                    offset  bits  flags
      { "fixup_ppc_br24",        2,      24,   MCFixupKindInfo::FKF_IsPCRel },
      { "fixup_ppc_br24_notoc",  2,      24,   MCFixupKindInfo::FKF_IsPCRel },
      { "fixup_ppc_brcond14",    2,      14,   MCFixupKindInfo::FKF_IsPCRel },
      { "fixup_ppc_br24abs",     2,      24,   0 },
      { "fixup_ppc_brcond14abs", 2,      14,   0 },
      { "fixup_ppc_half16",      0,      16,   0 },
      { "fixup_ppc_half16ds",    2,      14,   0 },
      { "fixup_ppc_pcrel34",     0,      34,   MCFixupKindInfo::FKF_IsPCRel },
      { "fixup_ppc_imm34",       0,      34,   0 },
      { "fixup_ppc_nofixup",     0,       0,   0 }
    };

    // Fixup kinds from .reloc directive are like R_PPC_NONE/R_PPC64_NONE. They
    // do not require any extra processing.
    if (Kind >= FirstLiteralRelocationKind)
      return MCAsmBackend::getFixupKindInfo(FK_NONE);

    if (Kind < FirstTargetFixupKind)
      return MCAsmBackend::getFixupKindInfo(Kind);

    assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() &&
           "Invalid kind!");
    return (Endian == llvm::endianness::little
                ? InfosLE
                : InfosBE)[Kind - FirstTargetFixupKind];
  }

  void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
                  const MCValue &Target, MutableArrayRef<char> Data,
                  uint64_t Value, bool IsResolved,
                  const MCSubtargetInfo *STI) const override {
    MCFixupKind Kind = Fixup.getKind();
    if (Kind >= FirstLiteralRelocationKind)
      return;
    Value = adjustFixupValue(Kind, Value);
    if (!Value) return;           // Doesn't change encoding.

    unsigned Offset = Fixup.getOffset();
    unsigned NumBytes = getFixupKindNumBytes(Kind);

    // For each byte of the fragment that the fixup touches, mask in the bits
    // from the fixup value. The Value has been "split up" into the appropriate
    // bitfields above.
    for (unsigned i = 0; i != NumBytes; ++i) {
      unsigned Idx =
          Endian == llvm::endianness::little ? i : (NumBytes - 1 - i);
      Data[Offset + i] |= uint8_t((Value >> (Idx * 8)) & 0xff);
    }
  }

  bool shouldForceRelocation(const MCAssembler &Asm, const MCFixup &Fixup,
                             const MCValue &Target,
                             const MCSubtargetInfo *STI) override {
    MCFixupKind Kind = Fixup.getKind();
    switch ((unsigned)Kind) {
    default:
      return Kind >= FirstLiteralRelocationKind;
    case PPC::fixup_ppc_br24:
    case PPC::fixup_ppc_br24abs:
    case PPC::fixup_ppc_br24_notoc:
      // If the target symbol has a local entry point we must not attempt
      // to resolve the fixup directly.  Emit a relocation and leave
      // resolution of the final target address to the linker.
      if (const MCSymbolRefExpr *A = Target.getSymA()) {
        if (const auto *S = dyn_cast<MCSymbolELF>(&A->getSymbol())) {
          // The "other" values are stored in the last 6 bits of the second
          // byte. The traditional defines for STO values assume the full byte
          // and thus the shift to pack it.
          unsigned Other = S->getOther() << 2;
          if ((Other & ELF::STO_PPC64_LOCAL_MASK) != 0)
            return true;
        } else if (const auto *S = dyn_cast<MCSymbolXCOFF>(&A->getSymbol())) {
          return !Target.isAbsolute() && S->isExternal() &&
                 S->getStorageClass() == XCOFF::C_WEAKEXT;
       }
      }
      return false;
    }
  }

  void relaxInstruction(MCInst &Inst,
                        const MCSubtargetInfo &STI) const override {
    // FIXME.
    llvm_unreachable("relaxInstruction() unimplemented");
  }

  bool writeNopData(raw_ostream &OS, uint64_t Count,
                    const MCSubtargetInfo *STI) const override {
    uint64_t NumNops = Count / 4;
    for (uint64_t i = 0; i != NumNops; ++i)
      support::endian::write<uint32_t>(OS, 0x60000000, Endian);

    OS.write_zeros(Count % 4);

    return true;
  }
};
} // end anonymous namespace


// FIXME: This should be in a separate file.
namespace {

class ELFPPCAsmBackend : public PPCAsmBackend {
public:
  ELFPPCAsmBackend(const Target &T, const Triple &TT) : PPCAsmBackend(T, TT) {}

  std::unique_ptr<MCObjectTargetWriter>
  createObjectTargetWriter() const override {
    uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(TT.getOS());
    bool Is64 = TT.isPPC64();
    return createPPCELFObjectWriter(Is64, OSABI);
  }

  std::optional<MCFixupKind> getFixupKind(StringRef Name) const override;
};

class XCOFFPPCAsmBackend : public PPCAsmBackend {
public:
  XCOFFPPCAsmBackend(const Target &T, const Triple &TT)
      : PPCAsmBackend(T, TT) {}

  std::unique_ptr<MCObjectTargetWriter>
  createObjectTargetWriter() const override {
    return createPPCXCOFFObjectWriter(TT.isArch64Bit());
  }

  std::optional<MCFixupKind> getFixupKind(StringRef Name) const override;
};

} // end anonymous namespace

std::optional<MCFixupKind>
ELFPPCAsmBackend::getFixupKind(StringRef Name) const {
  if (TT.isOSBinFormatELF()) {
    unsigned Type;
    if (TT.isPPC64()) {
      Type = llvm::StringSwitch<unsigned>(Name)
#define ELF_RELOC(X, Y) .Case(#X, Y)
#include "llvm/BinaryFormat/ELFRelocs/PowerPC64.def"
#undef ELF_RELOC
                 .Case("BFD_RELOC_NONE", ELF::R_PPC64_NONE)
                 .Case("BFD_RELOC_16", ELF::R_PPC64_ADDR16)
                 .Case("BFD_RELOC_32", ELF::R_PPC64_ADDR32)
                 .Case("BFD_RELOC_64", ELF::R_PPC64_ADDR64)
                 .Default(-1u);
    } else {
      Type = llvm::StringSwitch<unsigned>(Name)
#define ELF_RELOC(X, Y) .Case(#X, Y)
#include "llvm/BinaryFormat/ELFRelocs/PowerPC.def"
#undef ELF_RELOC
                 .Case("BFD_RELOC_NONE", ELF::R_PPC_NONE)
                 .Case("BFD_RELOC_16", ELF::R_PPC_ADDR16)
                 .Case("BFD_RELOC_32", ELF::R_PPC_ADDR32)
                 .Default(-1u);
    }
    if (Type != -1u)
      return static_cast<MCFixupKind>(FirstLiteralRelocationKind + Type);
  }
  return std::nullopt;
}

std::optional<MCFixupKind>
XCOFFPPCAsmBackend::getFixupKind(StringRef Name) const {
  return StringSwitch<std::optional<MCFixupKind>>(Name)
      .Case("R_REF", (MCFixupKind)PPC::fixup_ppc_nofixup)
      .Default(std::nullopt);
}

MCAsmBackend *llvm::createPPCAsmBackend(const Target &T,
                                        const MCSubtargetInfo &STI,
                                        const MCRegisterInfo &MRI,
                                        const MCTargetOptions &Options) {
  const Triple &TT = STI.getTargetTriple();
  if (TT.isOSBinFormatXCOFF())
    return new XCOFFPPCAsmBackend(T, TT);

  return new ELFPPCAsmBackend(T, TT);
}